The advent of blind fasteners, such as a toggle or Moly bolt, has facilitated the attachment of various items externally on a hollow wall. Since the fastening portion of a toggle bolt has a generally rectangular cross section upon collapse thereof, a rectangular hole must be formed in the wall to facilitate insertion of the toggle bolt therethrough. Such a procedure is time consuming and does not always provide a hole having the desired tolerances to assure firm securance of the toggle bolt to the wall. In particular, the hole requires a cross sectional area approximating eight times the cross sectional area of the bolt and since the critical area of stress is located closely adjacent to the hole, the holding efficiency of the toggle bolt becomes less as the hole becomes dimensionally larger.
In addition, the toggle bolt has a pair of pivoted prongs which extend radially outwardly from the nut attached thereto to absorb stresses and to anchor the bolt in place. Thus, the prongs provide limited bearing contact with the blind side of the wall and provide only limited absorption of stresses in a direction perpendicular to the longitudinal axis of the bolt. In short, the prongs essentially provide point contact with the blind side of the wall and the toggle bolt will tend to pull back through the wall when increased loads are imposed thereon in the aforementioned vertical direction. Furthermore, the toggle bolt depends upon a pivoting action which must be precisely controlled to assure contact with the blind side of the wall. In addition, the articulated components of the toggele bolt add to the manufacturing costs thereof over blind fasteners of the semistatic type.
The blind fastener of the Moly type exhibits similar shortcomings. In this type of fastener a bolt is threadably mounted in a nut secured to an end of a cylinder comprising a plurality of longitudinally disposed ribs which tend to spiral and bend in an axial direction upon retraction of the nut towards the head end of the bolt. As is well known in the fastening arts, such a blind fastener is difficult to install and oftentimes pulls outwardly through the hole formed through a wall upon which an item is desired to be attached. Furthermore, this rather complicated type of fastener is relatively expensive to manufacture.